The present invention generally concerns consolidation of metallic and nonmetallic powders or combinations thereof to form a consolidated body of predetermined density. The present invention more particularly concerns the consolidation of such powders at temperatures in excess of 1400 degrees Centigrade. The present invention also concerns a monolithic die material suitable for use in consolidating the powders at such temperatures.
Consolidated, or high density as a percent of theoretical density, ceramic-containing bodies are useful in applications such as cutting, drilling and shaping hard materials. Hard materials include rock, metals and metal alloys.
Powdered materials, e.g., ceramic powders, are consolidated by several known procedures. These procedures typically begin by cold pressing the powdered material into a preform. As an alternative, the powdered material is hermetically sealed in a can. The powdered material, either as a preform or as the contents of a hermetically sealed can, is then subjected to consolidation pressure. Pressure may be applied either by mechanical means such as a forging press or by gaseous means such as a gas at superatmospheric pressure.
U.S. Pat. No. 4,428,906 discloses a pressure-transmitting medium prepared from a mixture of borosilicate glass and a refractory powder. The refractory powder consists of magnesium oxide, ammonium dihydrogen phosphate and silica powder in the form of quartz and cristobalite. The borosilicate glass and refractory powders are mixed with water to form a slurry that is cast into the shape of a die. The refractory powder and water react at ambient temperatures to form magnesium ammonium phosphate hexahydrate which acts as a cement to bind the glass and silica powders. The phosphate decomposes to an amorphous phase upon heating to about 250.degree. Centigrade (.degree. C.) during drying. Further heating of the die to about 1100.degree. C. during preheating results in conversion of the amorphous phase to magnesium pyrophosphate or, if excess magnesium oxide is present, magnesium orthophosphate.
Dies prepared from the mixture of borosilicate glass and refractory powder provide satisfactory results at temperatures of from about 1100.degree. C. up to about 1400.degree. C. At higher temperatures, the magnesium phosphates react with the silica and glass to form magnesium silicates and volatile phosphorus oxides. Volatilization of the phosphorus oxides leaves behind a weakened, porous structure that is prone to premature collapse during handling. In addition, condensation of the phosphorus oxides on comparatively cooler surfaces within a heating furnace can lead to corrosion of furnace parts.
Some ceramic materials and cermets must be heated to temperatures in excess of 1400.degree. C., e.g., 1600.degree.-1975.degree. C., in order to attain densities approaching theoretical density. As such, it would be desirable if there were a pressure-transmitting medium or fluid die material which would allow use of such higher temperatures.